Printed circuit boards (hereinafter also referred to as PCBs), chip carriers, and the like (all referred to herein as “circuitized substrates”) are typically produced in laminate form in which several layered dielectric and conductive material members (laminates) are bonded together using conventional lamination processing involving relatively high temperatures and pressures. The conductive layers, typically of thin copper, are usually used in the formed substrate for providing electrical connections to and among various devices located on the surface of the substrate, examples of such devices being integrated circuits (semiconductor chips) and discrete passive devices, such as capacitors, resistors, inductors, and the like. Typically, these discrete passive devices occupy a high percentage of the surface area of the completed multi-layered substrate, which is obviously undesirable from a future design perspective due to the ever-present demand for miniaturization.
There have been various efforts to include multiple functions (e.g. resistors, capacitors and the like) within a single component adapted for being mounted on a substrate (e.g., PCB) in an attempt to increase the available upper substrate surface area (also often referred to as “real estate”). When passive devices are in such a configuration, these are often referred to collectively and individually as integral passive devices or the like, meaning that the functions are integrated into the singular component. Because of such external positioning, these components still utilize, albeit less than if in singular form, valuable board “real estate.” In response, there have been efforts to embed discrete passive components within the board. When so positioned, such components are also referred to as “embedded” passive components. A capacitor designed for disposition within (between selected layers of) a PCB (board) substrate may thus be referred to as an embedded integral passive component, or, more simply, an embedded capacitor. Such a capacitor thus provides internal capacitance. The result of this internal positioning is that it is unnecessary to also position such devices externally on the PCB's outer surface(s), thus saving valuable PCB real estate.
For an established capacitor area, two approaches are known for increasing the planar capacitance (capacitance/area) of an internal capacitor. In one such approach, higher dielectric constant materials can be used, while in a second, the thickness of the dielectric can be reduced. These constraints are reflected in the following formula, known in the art, for capacitance per area:C/A=(Dielectric Constant of Laminate×Dielectric Constant in Vacuum/Dielectric Thickness)where: C is the capacitance and A is the capacitor's area. Additional formulae are provided herein with respect to defining capacitance values for the structures formed herein.
As mentioned above, there have been previous attempts to provide internal capacitance and other internal conductive structures, components or devices (one good example being internal semiconductor chips) within circuitized substrates such as PCBs, some of these including the use of nano-powders. The cited U.S. Pat. Nos. 7,541,265 and 7,384,856 also define such approaches. The following documents also describe examples of such attempts, including some which discuss using nano-powders and those using alternative measures. Further, some of the patents listed below, and some of the pending applications cited above, mention the use of various materials for providing desired capacitance levels. With respect to the following patents, some mention or suggest problems associated with the methods and resulting materials used to do so.
In U.S. Pat. No. 7,064,412, entitled ELECTRONIC PACKAGE WITH INTEGRATED CAPACITOR and issued on Jun. 20, 2006, there is described an electronic package including a conductive trace layer having a first side and a second side. The conductive trace layer is patterned to define a plurality of interconnect pads. A flexible dielectric substrate is mounted on the first side of the conductive trace layer. A flexible capacitor including a first conductive layer, a second conductive layer and a layer of dielectric material disposed between the first and the second conductive layers is mounted with the first conductive layer adjacent the second side of the conductive trace layer. The first conductive layer of the capacitor is electrically connected to a first set of the interconnect pads and the second conductive layer of the capacitor is electrically connected to a second set of the interconnect pads. In this patent, a copper foil, or other conductive substrate, which may have material present on its surface such as an organic anti-corrosion agent (for example, a benzotriazole derivative) and residual oils from a rolling process, preferably, has a thickness of less than about 100 microns. The copper foil is subjected to a surface treatment to ensure adhesion between the dielectric layer and layers of copper foil. A blend of dielectric material may be prepared by providing a resin such as epoxy, optionally including dielectric or insulating particles such as barium titanate, and optionally including a catalyst for the epoxy. Absorbed water or residual materials on the particles, e.g., carbonates resulting from the manufacturing process, can be removed from the surface of the particles before use by heating the particles in air at a particular temperature for a period of time, for example, 350 degrees Celsius (also referred to herein at many locations simply as C) for fifteen hours. The blend of barium titanate particles and epoxy is prepared by mixing together barium titanate, a solvent solution of epoxies, e.g. ketone, and a dispersing agent. A high shear rotor-stator mixer (6000 rpm) with a water/ice bath is used, while ball-milling is another method. The blend is allowed to sit undisturbed allowing agglomerates to settle to the bottom of the container. The settling is allowed to occur for about twelve hours or more. As a final filtration step, the blend is then filtered, for example, through a stainless steel mesh filter or equivalent having a mesh size of from about two micrometers to about five micrometers. The blend may be coated onto the copper in a solvent system or solvent may be omitted if the organic binder is a liquid with sufficiently low viscosity to enable coating.
In U.S. Pat. No. 7,025,607, entitled CAPACITOR MATERIAL WITH METAL COMPONENT FOR USE IN CIRCUITIZED SUBSTRATES, CIRCUITIZED SUBSTRATE UTILIZING SAME, METHOD OF MAKING SAID CIRCUITIZED SUBSTRATE, AND INFORMATION HANDLING SYSTEM UTILIZING SAID CIRCUITIZED SUBSTRATE and issue Apr. 11, 2006, there is defined a material for use as part of an internal capacitor within a circuitized substrate in which the material includes a polymer resin and a quantity of nano-powders including a mixture of at least one metal component and at least one ferroelectric ceramic component, the ferroelectric ceramic component nano-particles having a particle size substantially in the range of between about 0.01 microns and about 0.9 microns and a surface within the range of from about 2.0 to about 20 square meters per gram. A circuitized substrate adapted for using such a material and capacitor therein and a method of making such a substrate are also defined. An electrical assembly (substrate and at least one electrical component) and an information handling system (e.g., personal computer) are also defined. U.S. Pat. No. 7,025,607 is assigned to the same Assignee as the present invention.
In U.S. Pat. No. 6,815,085, entitled PRINTED CIRCUIT BOARD CAPACITOR STRUCTURE AND METHOD and issued Nov. 9, 2004, there is described a capacitive element for a circuit board or chip carrier which is formed from a pair of conductive sheets having a dielectric component laminated there-between. The dielectric component is formed from two or more dielectric sheets, at least one of which can be partially cured followed by being fully cured. The partially cured sheet is laminated to at least one other sheet of dielectric material and one of the sheets of conductive material. The total thickness of the two sheets of the dielectric component does not exceed about four mils and preferably does not exceed about three mils. The use of two or more sheets of dielectric material makes it very unlikely that two or more defects in the sheets of dielectric material will align, thus greatly reducing the probability of a defect causing a failure in test or field use. In this patent, a pair of copper sheets are coated each on one side thereof with a dielectric material which may be epoxy or other type of dielectric material such as a cyanate ester, a polyimide, or polytetrafluoroethlyene (PTFE). The dielectric materials, other than the impregnated glass cloth, may be applied as liquids or, in the case of polyimide and PTFE, be in the form of free standing films of material. The material is partially cured or, in the case of films or glass cloth, may be applied to the copper in the partially cured form. The sheets of copper with the dielectric material thereon are laminated together to form a structure comprised of two sheets of copper separated by two sheets of fully cured dielectric material.
In U.S. Pat. No. 6,739,027, entitled METHOD FOR PRODUCING PRINTED CIRCUIT BOARD WITH EMBEDDED DECOUPLING CAPACITANCE and issued May 25, 2004, there is described a method for producing a capacitor to be embedded in an electronic circuit package comprising the steps of selecting a first conductor foil, selecting a dielectric material, coating the dielectric material on at least one side of the first conductor foil, and layering the coated foil with a second conductor foil on top of the coating of dielectric material. Also claimed is an electronic circuit package incorporating at least one embedded capacitor manufactured in accordance with the present invention. In this patent, pre-drilled or pre-etched copper conductor foils that have been coated with a dielectric material are in the form of voltage or ground planes. After coating with dielectric material, these are stacked up in alternate fashion (i.e. voltage/ground/voltage) and laminated together with other signal planes to create a final multi-layer circuit board. Other suitable conductor foils include copper-Invar-copper, Invar, aluminum, and copper pre-laminated to a dielectric. The dielectric coating may be standard liquid epoxy, polyimide, Teflon, cyanate resins, powdered resin materials, or filled resin systems exhibiting enhanced dielectric constants. Coating of the dielectric material onto the copper foil may be performed using roller, draw, powder or curtain coating, electrostatic or electrophoretic deposition, screen printing, spraying, dipping or transfer of a dry film. Once multi-layer laminated, the thickness of these coated films is not limited by a glass cloth material.
In U.S. Pat. No. 6,704,207, entitled DEVICE AND METHOD FOR INTERSTITIAL COMPONENTS IN A PRINTED CIRCUIT BOARD and issued Mar. 9, 2004, there is described a printed circuit board (PCB) which includes a first layer having first and second surfaces, with an above-board device (e.g., an ASIC chip) mounted thereon. The PCB includes a second layer having third and fourth surfaces. One of the surfaces can include a recessed portion for securely holding an interstitial component. A “via”, electrically connecting the PCB layers, is also coupled to a lead of the interstitial component. The described interstitial components include components such as diodes, transistors, resistors, capacitors, thermocouples, and the like. In what appears to be the preferred embodiment, the interstitial component is a resistor having a similar size to a “0402” resistor which has a thickness of about 0.014 inches.
In U.S. Pat. No. 6,638,378, entitled PASSIVE ELECTRICAL ARTICLE, CIRCUIT ARTICLES THEREOF, AND CIRCUIT ARTICLES COMPRISING A PASSIVE ELECTRICAL ARTICLE and issued on Oct. 28, 2003, there is described a passive electrical article comprising (a) a first self-supporting substrate having two opposing major surfaces, (b) a second self-supporting substrate having two opposing major surfaces, and (c) an electrically insulating or electrically conducting layer comprising a polymer and having a thickness ranging from about 0.5 to about 10 microns between the first and second substrate, wherein a major surface of the first substrate in contact with the layer and a major surface of the second substrate in contact with the layer have an average surface roughness ranging from about ten to about 300 nm and wherein a force required to separate the first and second substrates of the passive electrical article at a ninety degree peel angle is greater than about three pounds/inch (about 0.5 kN/m). Suitable resins for the electrically insulating or electrically conductive layer, which can be used to form a capacitor or a resistor, include epoxy, polyimide, polyvinylidene fluoride, benzocyclobutene, polynorbornene, polytetrafluoroethylene, acrylates, and blends thereof. Commercially available epoxies include those available from Shell Chemical Company, Houston, Tex., under the trade designation “Epon 1001F” and “Epon 1050.” Preferably, the resin can withstand a temperature that would be encountered in a typical solder reflow operation, for example, in the range of about 180 to about 290 degrees C. These resins may be dried or cured to form the electrically insulating or electrically conducting layer. Dielectric or insulating particles include barium titanate, barium strontium titanate, titanium oxide, lead zirconium titanate, and mixtures thereof. A commercially available barium titanate is available from Cabot Performance Materials, Boyertown, Pa., under the trade designation “BT-8”. Conductive particles may comprise conductive or semiconductive materials such as metal or metal alloy particles where the metal may be silver, nickel, or gold; nickel-coated polymer spheres; gold-coated polymer spheres (commercially available from JCI USA Inc., New York, N.Y., under product designation number “20 GNR4.6-EH”); graphite tantalum nitrides; tantalum oxynitride; doped silicon; silicon carbide; and metal silicon nitrides.
In U.S. Pat. No. 6,625,857, entitled METHOD OF FORMING A CAPACITIVE ELEMENT and issued Sep. 30, 2003, there is described a method of forming a capacitive element for a circuit board or chip carrier. The element is formed from a pair of conductive sheets having a dielectric component laminated there-between. The dielectric component is formed of two or more dielectric sheets, at least one of which can be partially cured followed by being fully cured. The lamination takes place by laminating a partially cured sheet to at least one other sheet of dielectric material and one of the conductive sheets. The total thickness of the two sheets of the dielectric component does not exceed about four mils and preferably does not exceed about three mils; thus, the single dielectric sheet does not exceed about two mils and preferably does not exceed about 1.5 mils. The conducting sheets are preferably copper, e.g., either 0.5 ounce or 1.0 ounce copper sheets. The sheets preferably have one surface roughened to improve adhesion to other materials. A pair of dielectric material sheets are provided and located between the copper sheets. The dielectric sheets are ultra thin sheets of glass cloth which have been impregnated with an epoxy and partially (B-stage) cured. This B-stage curing is accomplished by heating to about 100 degrees C. for five to twenty minutes. The epoxy resin may be phenolically hardened epoxy resin. Glass cloths impregnated with this type of resin are sold by the assignee of this invention under the registered trademark Driclad.
In U.S. Pat. No. 6,616,794, entitled INTEGRAL CAPACITANCE FOR PRINTED CIRCUIT BOARD USING DIELECTRIC NANOPOWDERS and issued Sep. 9, 2003, there is described a method for producing integral capacitance components for inclusion within printed circuit boards in which hydro-thermally prepared nano-powders permit the fabrication of dielectric layers that offer increased dielectric constants and are readily penetrated by micro-vias. In the method described in this patent, a slurry or suspension of a hydro-thermally prepared nano-powder and solvent is prepared. A suitable bonding material, such as a polymer, is mixed with the nano-powder slurry, to generate a composite mixture which is formed into a dielectric layer. The dielectric layer may be placed upon a conductive layer prior to curing, or conductive layers may be applied upon a cured dielectric layer, either by lamination or metallization processes, such as vapor deposition or sputtering.
In U.S. Pat. No. 6,574,090, entitled PRINTED CIRCUIT BOARD CAPACITOR STRUCTURE AND METHOD and issued Jun. 3, 2003, there is described a capacitive element for a circuit board or chip carrier and method of manufacturing the same. The structure is formed from a pair of copper sheets having a dielectric component laminated there-between. The dielectric component, e.g., resin-impregnated fiber glass (one example being a material sold under the trade name “Driclad” by the Assignee of the present invention) is formed of two or more dielectric sheets, at least one of which can be partially cured or softened followed by being fully cured or hardened. The lamination takes place by laminating a partially cured or softened sheet to at least one other sheet of dielectric material and one of the sheets of conductive material. The total thickness of the two sheets of the dielectric component does not exceed about four mils and preferably does not exceed about three mils; thus, the single dielectric sheet does not exceed about two mils and preferably does not exceed about 1.5 mils in thickness.
In U.S. Pat. No. 6,542,379, entitled CIRCUITRY WITH INTEGRATED PASSIVE COMPONENTS AND METHOD FOR PRODUCING and issued Apr. 1, 2003, there are described passive electrical components such as capacitors, resistors, inductors, transformers, filters and resonators which are integrated into electrical circuits utilizing a process which maximizes the utilization of the planar surfaces of the substrates for high density placement of active components such as logic or memory integrated circuits. The passive components are integrated into a conventional circuit board utilizing a photoimageable dielectric material. The dielectric is photoimaged and etched to provide one or more recesses or openings for the passive devices, and photo-vias interconnecting the inputs and outputs of the integrated circuit board. The electronic structure comprising at least one of the passive devices integrated into a photoimaged dielectric is described as well as the method of manufacturing the same.
In U.S. Pat. No. 6,524,352, entitled METHOD OF MAKING A PARALLEL CAPACITOR LAMINATE and issued Feb. 25, 2003, there is defined a parallel capacitor structure capable of forming an internal part of a larger circuit board or the like structure to provide capacitance therefore. Alternatively, the capacitor may be used as an inter-connector to interconnect two different electronic components (e.g., chip carriers, circuit boards, and semiconductor chips) while still providing desired levels of capacitance for one or more of said components. The capacitor includes at least one internal conductive layer, two additional conductor layers added on opposite sides of the internal conductor, and inorganic dielectric material (preferably an oxide layer on the second conductor layer's outer surfaces or a suitable dielectric material such as barium titanate applied to the second conductor layers). Further, the capacitor includes outer conductor layers atop the inorganic dielectric material, thus forming a parallel capacitor between the internal and added conductive layers and the outer conductors.
In U.S. Pat. No. 6,496,356, entitled MULTILAYER CAPACITANCE STRUCTURE AND CIRCUIT BOARD CONTAINING THE SAME AND METHOD OF FORMING THE SAME and issued Dec. 17, 2002, there is described a method of forming a capacitive core structure and of forming a circuitized printed wiring board from the core structure. The capacitive core structure is formed by providing a central conducting plane of a sheet of conductive material and forming at least one clearance hole in the central conducting plane. First and second external conducting planes are laminated to opposite sides of the ground plane with a film of dielectric material between each of the first and second external planes and the central conducting plane. At least one clearance hole is formed in each of the first and second external planes. A circuitized wiring board structure can be formed by laminating a capacitive core structure between two circuitized structures.
In U.S. Pat. No. 6,446,317, entitled HYBRID CAPACITOR AND METHOD OF FABRICATION THEREFOR and issue Sep. 10, 2002, there is described a hybrid capacitor associated with an integrated circuit package that provides multiple levels of excess, off-chip capacitance to die loads. The hybrid capacitor includes a low inductance, parallel plate capacitor which is embedded within the package and electrically connected to a second source of off-chip capacitance. The parallel plate capacitor is disposed underneath a die, and includes a top conductive layer, a bottom conductive layer, and a thin dielectric layer that electrically isolates the top and bottom layers. The second source of off-chip capacitance is a set of self-aligned via capacitors, and/or one or more discrete capacitors, and/or an additional parallel plate capacitor. Each of the self-aligned via capacitors is embedded within the package, and has an inner conductor and an outer conductor. The inner conductor is electrically connected to either the top or bottom conductive layer, and the outer conductor is electrically connected to the other conductive layer. The discrete capacitors are electrically connected to contacts from the conductive layers to the surface of the package. During operation, one of the conductive layers of the low inductance parallel plate capacitor provides a ground plane, while the other conductive layer provides a power plane.
In U.S. Pat. No. 6,395,996, entitled MULTI-LAYERED SUBSTRATE WITH A BUILT-IN CAPACITOR DESIGN and issued May 28, 2002, there is described a multi-layered substrate having built-in capacitors which are used to decouple high frequency noise generated by voltage fluctuations between a power plane and a ground plane of a multi-layered substrate. At least one kind of dielectric material, which has filled-in through holes between the power plane and the ground plane and includes a high dielectric constant, is used to form the built-in capacitors.
In U.S. Pat. No. 6,370,012, entitled CAPACITOR LAMINATE FOR USE IN PRINTED CIRCUIT BOARD AND AS AN INTERCONNECTOR and issued Apr. 9, 2002, there is described a parallel capacitor structure capable of forming an internal part of a larger circuit board or the like structure to provide capacitance there-for. Alternatively, the capacitor may be used as an inter-connector to interconnect two different electronic components (e.g., chip carriers, circuit boards, and even semiconductor chips) while still providing desired levels of capacitance for one or more of said components. The capacitor includes at least one internal conductive layer, two additional conductor layers added on opposite sides of the internal conductor, and inorganic dielectric material (preferably an oxide layer on the second conductor layer's outer surfaces or a suitable dielectric material such as barium titanate applied to the second conductor layers). Further, the capacitor includes outer conductor layers atop the inorganic dielectric material, thus forming a parallel capacitor between the internal and added conductive layers and the outer conductors.
In U.S. Pat. No. 6,343,001, entitled MULTILAYER CAPACITANCE STRUCTURE AND CIRCUIT BOARD CONTAINING THE SAME and issued Jan. 29, 2002, there is described a method of forming a capacitive core structure and of forming a circuitized printed wiring board from the core structure. The capacitive core structure is formed by providing a central conducting plane of a sheet of conductive material and forming at least one clearance hole in the central conducting plane. First and second external conducting planes are laminated to opposite sides of the ground plane with a film of dielectric material between each of the first and second external planes and the central conducting plane. At least one clearance hole is formed in each of the first and second external planes. A circuitized wiring board structure can be formed by laminating a capacitive core structure between two circuitized structures.
In U.S. Pat. No. 6,274,224, entitled PASSIVE ELECTRICAL ARTICLE, CIRCUIT ARTICLES THEREOF, AND CIRCUIT ARTICLES COMPRISING A PASSIVE ELECTRICAL ARTICLE and issued Aug. 14, 2001, there is described a passive electrical article comprising (a) a first self-supporting substrate having two opposing major surfaces, (b) a second self-supporting substrate having two opposing major surfaces, and (c) an electrically insulating or electrically conducting layer, wherein a major surface of the first substrate in contact with the layer and a major surface of the second substrate in contact with the layer have an average surface roughness ranging from about 10 to about 300 nm and wherein a force required to separate the first and second substrates of the passive electrical article at a ninety degree peel angle is greater than about three pounds/inch (about 0.5 kN/m). Dielectric materials possessing higher dielectric constants are used, as may be alternative perovskite class materials such as barium titanate (BaTiO3), lead-zirconium titanate (PZT), lead-manganese-niobium (PMN), lead titanate (PbTiO3) and strontium titanate (SrTiO3). Copper is used for the conductive layering.
In U.S. Pat. No. 6,256,850, entitled METHOD FOR PRODUCING A CIRCUIT BOARD WITH EMBEDDED DECOUPLING CAPACITANCE and issued Jul. 10, 2001, there is described a method for producing a capacitor to be embedded in an electronic circuit package comprising the steps of selecting a first conductor foil, selecting a dielectric material, coating the dielectric material on at least one side of the first conductor foil, and layering the coated foil with a second conductor foil on top of the coating of dielectric material. The conductor foil is copper, with other suitable conductor foils including copper-Invar-copper, Invar, aluminum, and copper pre-laminated to a dielectric. The dielectric coating may be any type of dielectric material from standard liquid epoxy, polyimide, Teflon, cyanate resins, powdered resin materials, or filled resin systems exhibiting enhanced dielectric constants. Coating of the dielectric material onto the conductor foil is performed with any number of methods known in the industry such as roller, draw, powder or curtain coating, electrostatic or electrophoretic deposition, screen printing, spraying, dipping or transfer of a dry film.
In U.S. Pat. No. 6,215,649, entitled PRINTED CIRCUIT BOARD CAPACITOR STRUCTURE AND METHOD and issued Apr. 10, 2001, there is described a capacitive element for a circuit board or chip carrier. The structure is formed from a pair of conductive sheets having a dielectric component laminated there-between. The dielectric component is formed of two or more dielectric sheets at least one of which can be partially cured or softened followed by being fully cured or hardened. The lamination takes place by laminating a partially cured or softened sheet to at least one other sheet of dielectric material and one of the sheets of conductive material. The use of two or more sheets of dielectric material is alleged in this patent to make it unlikely that two or more defects in the sheets of dielectric material will align, thus greatly reducing the probability of a defect causing a failure in test or field use.
In U.S. Pat. No. 6,207,595, entitled LAMINATE AND METHOD OF MANUFACTURE THEREOF and issued Mar. 27, 2001, there is described a fabric-resin dielectric material for use in a laminate structure and method of its manufacture. The resulting structure is adaptable for use in a printed circuit board or chip carrier substrate. The resin may be an epoxy resin such as is currently used on a large scale worldwide for “FR-4” composites. A resin material based on bismaleimide-triazine (BT) is also acceptable, this patent further adding that, more preferably, the resin is a phenolically hardenable resin material as is known in the art, with a glass transition temperature of about 145 degrees C.
In U.S. Pat. No. 6,150,456, entitled HIGH DIELECTRIC CONSTANT FLEXIBLE POLYIMIDE FILM AND PROCESS OF PREPARATION and issued Nov. 21, 2000, there is described a flexible, high dielectric constant polyimide film composed of either a single layer of an adhesive thermoplastic polyimide film or a multilayer polyimide film having adhesive thermoplastic polyimide film layers bonded to one or both sides of the film and having dispersed in at least one of the polyimide layers from 4 to 85 weight % of a ferroelectric ceramic filler, such as barium titanate or polyimide-coated barium titanate, and having a dielectric constant of from 4 to 60. The high dielectric constant polyimide film can be used in electronic circuitry and electronic components such as multilayer printed circuits, flexible circuits, semiconductor packaging and buried (internal) film capacitors.
In U.S. Pat. No. 6,068,782, entitled INDIVIDUAL EMBEDDED CAPACITORS FOR LAMINATED PRINTED CIRCUIT BOARDS and issued May 30, 2000, there is described a method of fabricating individual, embedded capacitors in multilayer printed circuit boards. The method is allegedly compatible of being performed using standard printed circuit board fabrication techniques. The capacitor fabrication is based on a sequential build-up technology employing a first pattern-able insulator. After patterning of the insulator, pattern grooves are filled with a high dielectric constant material, typically a polymer/ceramic composite. Capacitance values are defined by the pattern size, thickness and dielectric constant of the composite. Capacitor electrodes and other electrical circuitry can be created either by etching laminated copper, by metal evaporation or by depositing conductive ink.
In U.S. Pat. No. 5,972,053, entitled CAPACITOR FORMED WITHIN PRINTED CIRCUIT BOARD and issued Oct. 26, 1999, there is described a process for manufacturing a multi-layer printed circuit board utilizing layers including Ta and Hf and various other elements including Ta and Hf as part thereof for the board's layers. A capacitor may also be formed using this approach, according to the authors of this patent.
In U.S. Pat. No. 5,796,587, entitled PRINTED CIRCUIT BOARD WITH EMBEDDED DECOUPLING CAPACITANCE AND METHOD FOR PRODUCING SAME and issued Aug. 18, 1998, there is described a method for producing a capacitor to be embedded in an electronic circuit package comprising the steps of selecting a first conductor foil, selecting a dielectric material, coating the dielectric material on at least one side of the first conductor foil, and layering the coated foil with a second conductor foil on top of the coating of dielectric material.
In U.S. Pat. No. 5,162,977, entitled PRINTED CIRCUIT BOARD HAVING AN INTEGRATED DECOUPLING CAPACITIVE ELEMENT and issued Nov. 10, 1992, there is described a PCB which includes a high capacitance power distribution core, the manufacture of which is compatible with standard printed circuit board assembly technology. The high capacitance core consists of a ground plane and a power plane separated by a planar element having a high dielectric constant. The high dielectric constant material is typically glass fiber impregnated with a bonding material, such as epoxy resin loaded with a ferro-electric ceramic substance having a high dielectric constant. The ferro-electric ceramic substance is typically a nano-powder combined with an epoxy bonding material. According to this patent, the resulting capacitance of the power distribution core is sufficient to totally eliminate the need for decoupling capacitors on a PCB.
In U.S. Pat. No. 5,079,069, there is described a capacitor laminate which allegedly serves to provide a bypass capacitive function for devices mounted on the PCB, the capacitor laminate being formed of conventional conductive and dielectric layers whereby each individual external device is allegedly provided with capacitance by a proportional portion of the capacitor laminate and by borrowed capacitance from other portions of the capacitor laminate, the capacitive function of the capacitor laminate being dependent upon random firing or operation of the devices. That is, the resulting PCB still requires the utilization of external devices thereon, and thus does not afford the PCB external surface area real estate savings mentioned above which are desired and demanded in today's technology.
In U.S. Pat. No. 5,027,253, entitled CAPACITOR LAMINATE FOR USE IN CAPACITIVE PRINTED CIRCUIT BOARDS AND METHODS OF MANUFACTURE and issued Jan. 7, 1992, there is described a multilayer circuit package having a “buried” thin film capacitor. The circuit package includes at least a power core, a ground core, a first signal core, a second signal core, and the integral, buried, thin film capacitor. The integral, buried, thin film capacitor serves to capacitively couple the first and second signal cores. Structurally, the first signal core includes at least one first wire that terminates in at least one first electrode, while the second signal core includes at least one second wire that terminates in at least one second electrode. At least a portion of the first electrode overlays at least a portion of the first electrode overlays at least a portion of the second electrode and is separated there-from by a thin film of a dielectric material. The first electrode, the second electrode, and the thin film of dielectric material define the integral buried capacitor. The thin film capacitor is prepared by thin film methodology, with epitaxial deposition of the dielectric
In U.S. Pat. No. 4,945,399, entitled ELECTRONIC PACKAGE WITH INTEGRATED DISTRIBUTED DECOUPLING CAPACITORS and issued Jul. 31, 1990, there is described a semiconductor chip carrier which includes a plurality of distributed high frequency decoupling capacitors as an integral part of the carrier. The distributed capacitors are formed as a part of the first and second layers of metallurgy and separated by a layer of thin film dielectric material built up on a substrate. The distributed capacitors are positioned to extend from a ground pin of one of the layers of metallurgy to a plurality of mounting pads which are integral parts of the other of the layers of metallurgy. A semiconductor chip is mounted to the mounting pads and receives electrical power and signals there-through. The distributed capacitors decrease electrical noise associated with simultaneous switching of relatively large numbers of off-chip drivers which are electrically connected to the semiconductor chip.
Today's circuitized substrate manufacturers, responding to increasing demands for miniaturization, must provide decreasing signal line widths and thru-hole diameters in order to provide even greater circuit densities. Unfortunately, in doing so, they also confront many manufacturing problems. For example, some current processes utilize inner-layer materials that are typically glass-reinforced resin or other suitable dielectric material layers having a thickness of from about two to five mils, clad with metal (typically copper) on both surfaces. Glass-reinforcing material, typically utilizing continuous strands of fiberglass which extend throughout the width and length of the overall final substrates, is used to contribute strength and rigidity to the final stack. Being continuous, these strands commonly run the full width (or length) of the structure and include no breaks or other segments as part thereof. Such fibrous materials occupy a relatively significant portion of the substrate's total volume, a disadvantage especially when attempting to produce highly dense numbers of thru-holes and very fine line circuitry to meet new, more stringent design requirements.
More specifically, when holes are drilled (typically using laser or mechanical drills) to form these needed thru-holes, end segments of the fiberglass fibers may extend into the holes during lamination, and, if so, must be removed prior to metallization. This removal, in turn, creates the need for additional pretreatment steps such as the use of glass etchants to remove the glass fibrils extending into the holes, subsequent rinsing, etc. If the glass is not removed, a loss of continuity might occur in the internal wall metal deposit. In addition, both continuous and semi-continuous glass fibers add weight and thickness to the overall final structure, yet another disadvantage associated with such fibers. Additionally, since lamination is typically at a temperature above 150 degrees C., the resinous portion of the laminate may then shrink during cooling to the extent permitted by the rigid copper cladding, which is not the case for the continuous strands of fiberglass or other continuous reinforcing material used.
The strands thus take on a larger portion of the substrate's volume following such shrinkage and add further to complexity of manufacture in a high-density product. If the copper is etched to form a discontinuous pattern, laminate shrinkage may not be restrained even to the extent above by the copper cladding. Obviously, this problem is exacerbated as feature sizes (line widths and thicknesses, and thru-hole diameters) decrease. Consequently, even further shrinkage may occur. The shrinkage, possibly in part due to the presence of the relatively large volume percentage of continuous or semi-continuous fiber strands in the individual layers used to form a final product possessing many such layers, may have an adverse affect on dimensional stability and registration between said layers, adding even more problems for the PCB manufacturer.
The presence of glass fibers, especially those of the woven type, also substantially impairs the ability to form high quality, very small thru-holes, including when using a laser. Glass cloth has drastically different absorption and heat of ablation properties than typical thermoset or thermoplastic matrix resins. In a typical woven glass cloth, for example, the density of glass a laser might encounter can vary from approximately 0% in a window area to approximately 50% by volume or even more, especially in an area over a cloth “knuckle”. This wide variation in encountered glass density leads to problems obtaining the proper laser power for each thru-hole and may result in wide variations in thru-hole quality, obviously unacceptable by today's very demanding manufacturing standards.
Glass fiber presence also often contributes to an electrical failure mode known as CAF growth. CAF (cathodic/anodic filament) growth often results in an electrical shorting failure which occurs when dendritic metal filaments grow along an interface (typically a glass fiber/epoxy resin interface), creating an electrical path between two features which should remain electrically isolated. Whether continuous (like woven cloth) or semi-continuous (like chopped fiber mattes), glass fiber lengths are substantial in comparison to the common distances between isolated internal features, and thus glass fibers can be a significant detractor for PCB insulation resistance reliability. While the use of glass mattes composed of random discontinuous chopped fibers (in comparison to the longer fibers found in continuous structures) can largely abate the problem of inadequate laser drilled thru-hole quality, such mattes still contain fibers with substantial length compared to internal board feature spacing and, in some cases, offer virtually no relief from the problem of this highly undesirable type of growth.
The utilization of ground and pre-fired ceramic powders in the dielectric layer, including as substitutes for the above glass fibers, also generally poses obstacles for the formation of thru-holes between conductive layers of a PCB. Pre-fired and ground ceramic nano-powder particles have a typical dimension in the range of 500-20,000 nanometers (nm). Furthermore, the particle distribution in this range is generally rather broad, meaning that there could be a 10,000 nm particle alongside a 500 nm particle.
The distribution within the dielectric layer of particles of different size often presents obstacles to thru-hole formation where the thru-holes are of extremely small diameter, also referred to in the industry as micro-vias. Another problem associated with pre-fired ceramic nano-powders is the ability for the dielectric layer to withstand substantial voltage without breakdown occurring across the layer. Typically, capacitance layers within a PCB are expected to withstand at least 300 volts (V) in order to qualify as a reliable component for PCB construction. The presence of the comparatively larger ceramic particles in pre-fired ceramic nano-powders within a capacitance layer prevents extremely thin layers from being used because the boundaries of contiguous large particles provide a path for voltage breakdown. This is even further undesirable because, as indicated by the equation cited above, greater planar capacitance may also be achieved by reducing the thickness of the dielectric layer. The thickness is thus limited by the size of the particles therein.
Some commercially available dielectric powders which have been used in internal conductive structures such as mentioned in some of the above patents, among these being metal titanate-based powders (see, e.g., U.S. Pat. No. 6,150,456), are known to be produced using a high-temperature, solid-state reaction of a mixture of the appropriate stoichiometric amounts of oxides or oxide precursors (e.g., carbonates, hydroxides or nitrates) of barium, calcium, titanium, and the like. In such calcination processes, the reactants are wet-milled to accomplish a desired final mixture. The resulting slurry is dried and fired at elevated temperatures, sometimes as high as 1,300 degrees C., to attain the desired solid state reactions.
Thereafter, the fired product is milled to produce a powder. Although the pre-fired and ground dielectric formulations produced by solid phase reactions are acceptable for many electrical applications, these suffer from several disadvantages. First, the milling step serves as a source of contaminants, which can adversely affect electrical properties. Second, the milled product consists of irregularly shaped fractured aggregates which are often too large in size and possess a wide particle size distribution, 500-20,000 nm. As a result, films produced using these powders are limited to thicknesses greater than the size of the largest particle. Thirdly, powder suspensions or composites produced using pre-fired ground ceramic powders typically must be used immediately after dispersion, due to the high sedimentation rates associated with large particles.
The stable crystalline phase of barium titanate for particles greater than 200 nm is tetragonal and, at elevated temperatures, a large increase in dielectric constant occurs due to a phase transition. It is thus clear that methods of making PCBs which rely on the advantageous features of using nano-powders as part of the PCB's internal components or the like, such as those described in selected ones of the above patents, possess various undesirable aspects which are detrimental to providing a PCB with optimal functioning capabilities when it comes to internal capacitance or other electrical operation. This is particularly true when the desired final product attempts to meet today's miniaturization demands, including the utilization of high density patterns of thru-holes therein.
In view of the above, it is believed that a method of making a circuitized substrate having therein a capacitor which obviates many of the problems described above would constitute a significant advancement in the art.